THURSDAY, Aug. 23 (HealthDay News) -- People at higher risk of developing
colorectal cancer may be able to reduce their risk by getting thorough colonoscopies and adhering to recommendations for follow-up exams, a new study suggests.

Researchers in Germany looked at more than 400 people with polyps -- growths in the colon and rectum that can lead to cancer -- that had been detected in the past 10 years. About a third of them developed colorectal cancer.

The researchers found that those with colorectal cancer were more likely to have neglected getting a follow-up colonoscopy within five years of detection and to not have had their polyps completely removed upon detection.

These colonoscopy-related factors accounted for two in five cancer cases, whereas factors related to the polyps themselves, such as the number of polyps a patient had, were only associated with one in five cases, the researchers said.

The study was conducted by researchers at the German Cancer Research Center and the University of Heidelberg, and was published in the Aug. 21 issue of the journal Annals of Internal Medicine.

"This study found that incomplete removal of polyps at colonoscopy in patients with a history of precancerous polyps and lack of follow-up colonoscopy within five years were the most important factors linked to subsequent development of colorectal cancer," said Dr. Frank Sinicrope, a gastroenterologist and medical oncologist at the Mayo Clinic in Rochester, Minn. Sinicrope was not involved in the research.

"Not achieving these objectives can result in failure to realize the full potential of colonoscopy to prevent colorectal cancer," Sinicrope added.

The German study involved 155 participants who had been diagnosed with colorectal cancer and 260 participants who, although they had at least one polyp detected, did not have colorectal cancer. More than 60 percent of the participants were 70 years old or older. Two-thirds were men.

The group found that participants who developed cancer were almost four times as likely as those who did not to still have some of their polyps, and about three times as likely to have let at least five years go by without a follow-up colonoscopy.

In contrast, the only characteristic of polyps that was associated with cancer risk was having at least three detected, which was twice as likely in the group that developed colorectal cancer.

Larger polyps were not associated with greater colorectal cancer risk in this study, and that may be because they are easier for the doctor to remove, according to Dr. Jeffrey Meyerhardt, an oncologist at the Dana-Farber Cancer Institute in Boston.

The study also found that the association between colorectal cancer and waiting more than five years for a follow-up colonoscopy was particularly strong for participants who were under 70; this group was more than six times as likely to have cancer.

It also is critical for younger patients to adhere to follow-up recommendations, Sinicrope said.

Patients also should take an active role in ensuring they get good colonoscopies, Meyerhardt added.

"It's a reasonable question to ask the person doing your colonoscopy: 'Have you done a lot of these in the past?'" he said. "If [your doctor] only practices them very infrequently and does a scope once a month, that may be an issue."

After the procedure, "discuss with the doctor ... how good of a colonoscopy they did and if they were satisfied they could see everything," Meyerhardt said. "If [a polyp] was removed, what were the characteristics and when should follow-up be?"

A follow-up or surveillance colonoscopy is important even if polyps were completely cut out because "somebody who makes polyps has a tendency to make more polyps in the future," Meyerhardt explained.

The American Cancer Society advises that people who have one or two small precancerous polyps detected should have another colonoscopy within five to 10 years, while those who had more than two small polyps or at least one large polyp detected should get a follow-up test after about three years.

The American Cancer Society estimates that there will be about 140,000 new cases of colon and rectal cancer in 2012. Colorectal cancer is the second most common cause of cancer-related death in the United States.